1. Field of the Invention
The subject invention relates to electrical circuitry and electrooptical systems and, more specifically, to electrode structures, solid-state light gate structures, preformed panel circuit arrangements and similar articles of manufacture, methods of increasing feasible electrode density in electrode structures, methods of providing electrically switchable light gate structures, and light gate utilization methods and apparatus.
2. Disclosure Statement
This disclosure statement is made persuant to the duty of disclosure imposed by law and formulated in 37 CRF 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art, inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material.
A feasibility of dense electrode arrys is fundamental to a provision or improvement of many electrooptical systems and various other apparatus. In particular, there are many areas of utility wheren spaced parallel electrodes, or interdigitated first and second electrodes, require an individual electrical connection at least to each electrode of the same kind.
Reference may, in this connection, be had to U.S. Pat. No. 3,124,635, by E. M. Jones et al, issued Mar. 10, 1964 and U.S. Pat. No. 4,010,376, by Sherman W. Duck, issued Mar. 1, 1977.
As to nature and utility of prior-art electrode devices, reference may also be had to U.S. Pat. Nos. 2,670,402, 2,836,766, 2,883,582, 2,898,489, 2,909,973, 2,928,993, 2,972,076, 2,988,647, 2,996,623, 3,069,973, 3,078,373, 3,082,327, 3,087,087, 3,087,985, 3,121,861, 3,137,762, 3,173,745, 3,220,012, 3,221,335, 3,265,928, 3,288,602, 3,312,825, 3,318,997, 3,341,692, 3,369,251, 3,400,382, 3,437,815, 3,449,038, 3,512,158, 3,540,427, 3,704,512, 3,732,424, 3,873,187 and 3,955,190, as well as to the article by Louis Mirando et al, entitled Flat Screen Television Takes Two Giant Steps Forward, ELECTRONICS, May 25, 1970, pp. 112 et seq.
An interesting proposal has been advanced by Mohan in U.S. Pat. No. 3,084,301, issued Apr. 2, 1963 in connection with an electrode structure for a scanning apparatus. Briefly, Mohan, in one embodiment, provides a common electrode in a serpentine or square-wave fashion between interdigitated first and second electrodes connected to opposite poles of a direct-current source.
Unfortunately, as Mohan himself points out, this in practice leads to a keystoning effect in the output amplitude of the switched current. The remedy proposed by Mohan, namely the provision of several parallel leads or terminals in place of a single common electrode terminal would largely neutralize an advantage that might be gained by using the Mohan electrode configuration. Also, the serpentine electrode meandering between opposite interdigitated electrodes provides a high reactance, notably a high inductance which diminishes the value of the structure as a switching device.
The need for high-density switching electrode structures has intensified with the development of electrooptical light gate systems in light modulators and other equipment as has been disclosed in U.S. Pat. Nos. 2,591,701, 3,027,806, 3,322,485, 3,354,465, 3,454,771, 3,464,762, 3,471,863, 3,492,492, 3,499,702, 3,499,704, 3,512,864, 3,567,847, 3,582,957, 3,597,044, 3,612,656, 3,624,597, 3,644,017, 3,657,471, 3,657,707, 3,666,666, 3,699,242, 3,702,724, 3,718,723, 3,737,211, 3,781,783, 3,787,111, 3,799,647, 3,823,998, 3,867,571, 3,914,546, 3,922,485, 3,926,520, 3,930,119, 3,944,323 and 3,945,715. For information on electro-optical oscillographs and facsimile equipment, reference may also be had to German Pats. Nos, 357 299, issued Aug. 19, 1922, 492 331, issued Mar. 5, 1930 and 584 384, issued Sep. 19, 1933 and to German published Patent Applications Nos. 2 321 870, published Nov. 7, 1974 and 2 322 473, published Nov. 21, 1974.
While the familiar Kerr cell naturally was spawned a multitude of proposals built on the light modulating capability of that cell, a more recent impetus in that direction has emanated from the advent of suitable light-modulating solid state materials as may be seen from U.S. Pat. Nos. 2,892,955, 2,911,370, 2,985,700, 4,144,411, 3,283,044, 3,303,133, 3,344,073, 3,429,818, 3,434,122, 3,464,924, 3,517,093, 3,531,182, 3,532,628, 3,536,625, 3,622,226, 3,630,597, 3,684,714, 3,699,044, 3,708,438, 3,728,263, 3,732,117, 3,744,875, 3,816,750, 3,826,865, 3,856,693, 3,871,745, 3,903,358, 3,917,780, 3,923,675, 3,932,313, 3,938,878 and 3,963,630 and U.S. published patent application B No. 384,225, dated Mar. 16, 1976.
A family of ferroelectric electro-optic ceramics is known as PZT compounds with P standing for lead, Z for zirconium and T for titanium. Under the influence of an electrical field, PZT compounds become birefringent and exhibit various electrooptic properties. For instance, incoming light is resolved into two component waves propagating at different velocities and in polarization planes that are at right angles to each other. The magnitude of the effect is a function of the applied voltage and of the light frequency. Light valves and gates may be provided by placing the electrooptic ceramic between a polarizer plate and an analyzer plate.
A breakthrough occurred with the discovery that substitution of small amounts of lanthanum greatly improves ferroelectric properties. These improved compounds generally have become known as PLZT compounds, with the L standing for lanthanum.
Reference may in this respect to had to Land et al, Ferroelectric Ceramic Electrooptic Materials and Devices, 57 Proceedings IEEE No. 5, May 1969, pp. 751 and 768, Thacher et al, Ferroelectric Electrooptic Ceramics with Reduced Scattering, Ed-16, IEEE Transactions on Electron Devices, No. 6, June 1969, pp. 515 to 521, Maldonado et al, Ferroelectric Ceramic Light Gates Operated in a Voltage-Controlled Mode, ED-17, IEEE Transactions on Electron Devices, No. 2, February 1970, pp. 148 to 157, New Ferroelectric Ceramics Enhance Electro-Optic Performance, Design News, June 22, 1970, pp. 10 and 11, Haertling et al, Hot-Pressed (Pb, La) (Zr, Ti) O.sub.3 Ferroelectric Ceramics for Electrooptic Applications, 54 Journal of The American Ceramic Society, No. 1, January 1971, pp. 1 to 11, Waterworth et al, Integrated Electro-Optic Modulator Arrays, 4 Opto-elctronics (1972) 339 and 340, Cutchen et al, Electrooptic Devices Utilizing Quadratic PLZT Ceramic Elements, 30, 1973, Wescon Technical Papers, Vol. 17 pp. 1 to 12, Zook, Light Beam Deflector Performance: a Comparative Analysis, 13 APPLIED OPTICS, No. 4, April 1974, pp. 875 et seq., Fiber Display Features Digital Scanning, Optical Spectra, June 1974, and Cutchen et al, PLZT Electrooptic Shutters: Applications, 14 APPLIED OPTICS, No. 8, August 1975, pp. 1866 to 1873.
In the course of such development, devices such as Kerr cells in such applications as constant-density trace oscillographs disclosed in U.S. Pat. No. 3,354,465 by Merrit et al, issued Nov. 21, 1967, were replaced by solid-state light valves. Indeed, solid-state shutter systems were among the first practical applications as may, for instance, be seen from U.S. Pat. No. 3,555,987, by Iben Browning, issued Jan. 19, 1974. The switching properties and modes of ferroelectric ceramic plates were recognized and published such as in the above mentioned 1969 IEEE article by Land et al, pp. 61 and 762 and FIG. 20, and proposals for practical applications such as those suggested in the above mentioned U.S. Pat. No. 3,930,119, by Schmidt et al, issued Dec. 30, 1975, naturally followed.
In particular Schmidt et al propose in all their electrode structure embodiments attachment of the electric voltage-applying leads to the electrodes themselves. In this respect, reference may be had to the article by J. Thomas Cutchen et al, entitled Electrooptic Devices Utilizing Quadratic PLZT Ceramic Elements, published in 1973 WESCON Technical Papers, Vol. 17, Pt. 30/2, pp. 1 to 12. This publication in FIG. 19 shows dual aperture gate and single aperture gate structures and on page 10 mentions electrode widths of 0.001 to 0.003 inches and gap or gate widths between adjacent electrode pairs of 0.0015 to 0.002 inches, in PLZT devices.
With such an electrode structure, implementation of the above mentioned Schmidt et al disclosure would require wire sizes of 0.001 inch in diameter or less and bonding techniques which do not require more lateral space or do not leave a wider deposit than the diameter of the wire itself.
This in practice would require use of a wire of 0.001 inch in diameter or less, applied to each electrode by a special technique, such as wedge bonding, for the 0.001 electrode width.
With the dimensions given above, the center-to-center distances between the electrode terminals would have to be 0.005 inches, providing 200 gates per inch which would require 200 wires per inch to be individually bonded to electrode terminals. This is in line with Schmidt et al who mention 800 picture elements per line across a DIN A4 format paper.
In practice, such wire and terminal densities would be difficult enough to implement just in view of the requisite small wire size itself. However, the problem is greatly aggravated by the fact that every wire feeding or bonding tool inevitably has lateral dimensions exceeding significantly the wire diameter. This so far has precluded a practical implementation of the Schmidt et al and Cutchen proposals.
For a realization of such and similar proposals, a further hurdle that would have to be overcome stems from the widespread necessity of having to interface light gate structures or electrode arrangements with appropriate circuitry for driving the light gate or electrode system. In this respect, the best connecting system would be one in which the wires or leads run parallel to each other from the light gate or electrode structure to the driving circuit boards. This would at least tend to avoid the difficulty of having to provide and install insulated wires, or to insulate installed wires, having a diameter on the order of 0.001 inch or less.
For connecting wires to run parallel to each other, line densities on the driving circuit board side becomes similar to the requisite prior-art high terminal densities on the light gate or electrode structure side. This, in turn, would create considerable difficulties, since circuit boards still are typically made by thick film techniques which do not permit the line width and close electrode spacing achievable by thin film techniques. In consequence, more complex and expensive multilayer structures would have to be resorted to at the driving circuit boards.
No effective solution of these problems is offered in the available patent or other literature. For instance, the above mentioned Jones et al U.S. Pat. No. 3,124,635, like Schmidt et al, discloses electrode terminals of a center-to-center spacing no larger than the spacing between adjacent electrodes. In particular, Jones et al fail to gain any contact area or terminal spacing from their manner of locating their electrode terminals.
Raffel in U.S. Pat. No. 3,452,342 achieves center-to-center distances between adjacent terminals greater than the center-to-center spacing between corresponding electrodes connected to such terminals. In particular, Raffel achieves such an advantage by clustering or nesting terminals belonging to a given electrode array and by alternatingly providing terminals on opposite sides of the electrode arrays. This clustering or nesting, however, has the severe disadvantage in practice of necessitating a multitude of detrimental crossovers between terminals and connecting wires.
For instance, a wire lead connecting one of the innermost terminals of Raffel to appropriate energizing or driving circuitry would have to cross over a minimum of two other terminals. This, in practice, not only encumbers the job of establishing the requisite connections between the clustered terminals and the driving circuitry, but also creates a danger of faulty performance from unintended electrical contact of, or leakage between, crossing leads or leads crossing terminals.
The gravity of such problems can, for instance, be appreciated from a consideration of the Scarrott U.S. Pat. No. 3,449,038, requiring the provision of a multitude of connecting lead cross-overs for an implementation of its illustrated preferred embodiment.
Another article by J. Thomas Cutchen et al, entitled PLZT Electrooptic Shutters: Applications, published in APPLIED OPTICS, Vol. 14, No. 8 (August 1975), pp. 1866 et al, proposes in FIG. 2 an arrangement of terminals of alternate electrodes on opposite sides of the electrode array. This, indeed, would appear to double the achievable center-to-center distance between adjacent terminals relative to their corresponding electrodes. However, since suitable available driving circuitry typically is packaged or provided in terms of binary systems, in which driving transistors and similar components are grouped according to a power on the base of two, such as 2.sup.3, this Cutchen proposal would be rather impractical in its attempted implementation.
A somewhat related problem that has plagued the development of electrooptical solid-state light gate structures stems from the rather high voltages required to achieve rapid and reliable switching of the solid-state light gates. In this respect, both of the above mentioned Cutchen et al articles provide on a PLZT electrooptic ceramic substrate a plurality of interdigitated first and second electrodes and further provide a first common terminal interconnecting all first electrodes and a second common terminal interconnecting all second electrodes. All interconnected first and second electrodes are then simultaneously driven via the common first and second terminals. However, in their U.S. Pat. No. 3,744,875, Haertling et al explicitly deprecate such an approach in favor of a provision of transparent electrodes coating major surfaces of the solid-state plate to be switched.
For completeness' sake, reference is also made to U.S. Pat. No. 3,868,608, which shows a surface wave filter having interdigitated comb electrodes, and to a publication Insulation/Circuits, February 1979, p. 32, which shows similar interdigitated comb structures on a test board for measurement of insulation resistance degradation. No teaching of any solution to the problems herein set forth is, however, seen from these references.
Symptomatic in this respect appears to be the recently published United Kingdom Patent Specification No. 1 534 027, by Battelle Memorial Institute, which, in the context of an electrooptical modulator device, retrogresses to the type of electrode structures shown in FIGS. 1 and 2 of the above mentioned Jones et al U.S. Pat. No. 3,124,635.